With the rise of subscription TV services, a number of systems have been developed which will scramble the outgoing TV signals so that only those subscribers having an extra cost descrambler will be able to view programs on that channel. The prior art contains a number of devices which will descramble the incoming TV signals. Tese converter/descramblers typically receive a multi-channel input signal from a cable TV drop having both scrambled and unscrambled channels. Some or all of the scrambled channels are descrambled, depending upon what channels the subscriber is authorized to receive. All of the TV signals are output from the converter/descrambler on a single channel, typically channel 2, 3 or 4.
In order for the subscriber to view any cable television programs, he must tune his TV to the channel on which the converter/descrambler outputs the television signals (e.g., channel 2, 3 or 4). The subscriber's television set is left on this channel, and program channel selection is accomplished by using the tuner which is built into the cable TV converter/descrambler.
The use of a conventional converter/descrambler requires the additional expense of a tuner supplemental to the one already present in the subscriber's TV. Further, the single channel output nature of a conventional converter/descrambler is notoriously user unfriendly. Interfacing with other subscriber video equipment, such as a VCR, is quite complicated and can be exasperating to the subscriber. An outline of the problem can be found in commonly owned U.S. patent application no. 877,349 entitled "A VCR Interface for Receiving Cable TV Signals", now abandoned.
Initially, TV sets were equipped with a tuner receiving a limited number of cable TV channels. However, modern cable-ready TV sets and VCR units are now equipped with a tuner which can receive upwards of 70 channels, far exceeding the number of signal channels actually available to the subscriber. Some cable TV systems provide less than 20 channels. A typical system has 30-35 channels. Very few have in excess of 50 channels, although systems are available which have as many as 77 channels. Even though cable-ready television sets can tune in all of the channels a cable system offers, they cannot descramble premium channels. Thus, each TV set must be equipped by the cable system operator with a separate descrambler to provide viewing of premium programming. Most conventional converter/descramblers do not enable the utilization of many features provided in a cable-ready television set (e.g., remote volume control, audio muting, favorite channel programming, picture-in-a-picture, etc.), since the TV must always remain tuned to the output channel of the converter/descrambler. As a result, a subscriber must keep track of and use two separate remote control units to control both the TV and the converter/descrambler.
The single channel output of prior art converter/descramblers was mandated in part because it is not practical, and is often impossible, to remove a scrambled channel or channels from a contiguous set of channels, descramble the channel and reinsert it in unscrambled form back into the same channel assignment from whence it came. This is primarily due to the extremely stringent filtering requirements of TV signals. It is not presently possible to economically filter TV signals such that a first channel is totally separate from its adjacent channels without distorting the removed or remaining channels, or both.
It would be advantageous to provide an economical system for removing premium (i.e., scrambled) channels from a cable television signal, descramble those channels which a subscriber is authorized to view, and reinsert the channels in descrambled form back into the cable signal which is input to the subscriber's television set (or other video appliance). In this manner, the subscriber could view all unscrambled and authorized scrambled channels transmitted via the cable system without the need to use a separate tuner provided by the cable service provider. The subscriber could use the tuner in his cable-ready video appliance to tune to all channels directly, including the premium channels he is authorized to receive.
The present invention provides such a system.